The present invention relates to a froth flotation process for the recovery of mineral values from base metal and precious metal ores. More particularly, it relates to a new and improved process for beneficiating minerals by froth flotation incorporating a new class of depressants.
Certain theory and practice state that the success of a flotation process depends to a great degree on reagents called collectors that impart selective hydrophobicity to the mineral value which has to be separated from other minerals.
Certain other important reagents, such as the modifiers, are also largely responsible for the success of flotation separation of minerals. Modifiers include all reagents whose principal function is neither collecting nor frothing, but one of modifying the surface of the mineral so that the collector either adsorbs to it or does not. Modifying agents may thus be considered as depressants, activators, pH regulators, dispersants, deactivators, etc. Often, a modifier may perform several functions simultaneously.
In addition to attempts at making the collectors more selective for value minerals, other approaches to the problem of improving the flotation separation of value minerals have included the use of modifiers, more particularly depressants, to depress hydrous, layered silicates such as talc and other gangue minerals so that they do not float in the presence of collectors, thereby reducing the levels of non-value contaminants reporting to the concentrates. As has been mentioned above, a depressant is a modifier reagent which selectively adsorbs onto certain unwanted minerals thus making them hydrophilic and unable to float. Depressants can also prevent or inhibit adsorption of the collectors onto certain of the mineral particles surfaces present in the flotation slurry or pulp.
Hydrated silicates such as talc, i.e., magnesium silicate, which, because of their crystalographic structure, behave as a hydrophobic mineral when ground and slurried with water. The silicates therefore cause problems when associated with ores or minerals that contain value metals such as gold, platinum, nickel, zinc, lead and copper which are to be recovered by froth flotation. In the flotation of such hydrous, layered silicates as talc and pyrophyllite, depressants such as guar gum, starch, dextrin and carboxymethylcellulose have been found to be useful commercially. Guar gum and carboxymethylcellulose are the only two widely employed, with the guar gum the most common depressant for talc by far. These conventional depressants, however, represent a number of serious problems and have serious shortcomings attendant with their use. Guar gum, for example, is difficult to dissolve. Moreover, the conventional depressants are either non-selective or, when used in sufficient quantities to provide good separation, provide economically unsatisfactory concentrates, i.e., the yield of value minerals is too low.
The benefication criteria for treating complex ores are maximum recovery of value metal and precious metals (if any are present) and minimum contamination of the value concentrate by non-value hydrous, layered silicates such as talc. In many cases, these criteria cannot be met without seriously sacrificing value metals production or recovery. Therefore, there remains an urgent need for flotation reagents that can selectively depress talc reporting to the concentrate and concurrently provide economically acceptable recoveries of value minerals.
K. F. Lin etal; Surfactant Sci. Ser.; 1988; Polymeric Depressants; 27 (Reagents Miner, Technol.) pgs. 471-483 (Eng.); Hercules, Inc. Wilmington, Del. teach the use of polysaccharides as depressants and show specifically dihydroxpropylcellulose as a depressant for clay slime in a potash ore. The depressant was found to be intermediate to guar and starch for depressing clay. The process of the instant invention, however, relates to the beneficiation of value minerals from hydrophobic sulfide ores. Whereas potash ores are treated with long chain oxhydryl or cationic collectors which function by physical adsorption onto the potash (KCl) and float it, and the depressant stops the collector from adsorbing on the clay slimes present, such as kaolinite, sulfide ores are treated with sulfhydryl anionic collectors which function by chemical adsorption onto the sulfide mineral and float it and the depressant stops the collector from adsorbing onto the hydrous silicate (talc) and ferrous sulfide present. Thus, the use of 2,3-dihydroxypropylcellulose as a depressant in potash ore flotation would not suggest to one skilled in the art to utilize the instant depressants in sulfide ore flotation because of the dissimilarities of the two systems regarding collector functionality.
Unexpectedly, in view of the foregoing, it has now been discovered that dihydroxyalkyl polysaccharides are very selective depressants for hydrous, layered silicates. The use of the dihydroxyalkyl saccharides of the present invention provide a substantial reduction in talc contamination in the mineral concentrates reporting to the smelters and are more readily dissolved in water, i.e they have a more rapid hydration time than guar gum, and also provide maximum recovery of values from ores.